Testbed Setup

Our testbed deployment is based on the TWIST architecture originally developed by the Telecommunications Networks Group (TKN) at the Technical University of Berlin and significantly enhanced by the Cyber-Physical Systems Laboratory (CPSL) at the Washington University in St. Louis. The testbed is hierarchical in nature, consisting of three different levels of deployment: wireless devices, switches, and a desktop class server. A high level view of this three tiered architecture can be seen in the figure below on the left. At the lowest tier, wireless devices are placed throughout the physical environment in order to take sensor readings and/or perform actuation. Each wireless device, as shown in the figure below on the right, is an embedded computer (i.e., Raspberry Pi 3 Model B with WiFi and Bluetooth radios) integrating with a sensor node (i.e., TelosB mote with a ZigBee radio and temperature, humidity and light sensors) and a Power over Ethernet (PoE) splitter. The TelosB mote is connected to the Raspberry Pi through a USB cable. Messages can be exchanged between them over this interface in both directions. The wireless devices are powered by PoE and connected to the PoE switches in the second tier through Ethernet cables.

At the third and final tier exists a dedicated server which connects to the PoE switches through an Ethernet cable. This server is used to host, among other things, a database containing information about the different TelosB motes and Respberry PIs they are connected to. This database minimally contains information about the connections that have been established between the TelosB motes and Respberry PIs, as well as their current locations. The server is also used to provide a workable interface between the testbed and any end-users. Users may log onto the server to gain access to the information contained in the testbed database, as well as exchange messages with nodes contained in the testbed. The entire testbed architecture is based on cheap, off-the-shelf hardware and uses open-source software at every tier of its deployment.

A key capability of our testbed is a wired backplane network that can be used for managing wireless experiments and measurements without interfering with wireless communication. For example, log messages from individual device can be sent to the server over the wired connection without interfering with an application running in the wireless network. The wired infrastructure essentially provides an out of band means for collecting important information from each device without clogging up the wireless channel and adversely affecting any experiments being run. This log information can also be time stamped by the device using Network Time Protocol (NTP) in order to gather statistics about what is going on at each individual device in the network at any given time. Programming of wireless devices in the testbed is also made easier using the three tiered architecture, as a user simply tells the server which device it would like to program, and the server does the work of distributing this request to the proper device.

Individual device in the testbed can also be disabled or enabled. This capability allows node failures to be simulated in the testbed environment, as well as fine tune the density of the network itself when running certain types of experiments. The introduction of new nodes into the network can also be simulated by enabling nodes at specific times during the run of an experiment.

All of the features described above really boil down to just one thing. It is possible to run sophisticated experiments in the testbed without ever having to physically change the layout of the testbed or interact with the individual sensor nodes that make it up. Everything is controllable from the central server, and scripts can be written to perform countless numbers of operations involving each of the capabilities described above.

Existing Deployment

Currently the testbed consists of 50 wireless devices placed throughout the G-area of the Engineering Building. The figure below shows the placement of the devices in the testbed.

The testbed topology (ZigBee links) with a transmission power of -25 dBm, -15 dBm, and -10 dBm:

Here are some photos of the deployed devices:

IMPORTANT:
Please keep in mind that the devices deployed in the testbed only contain sensors for light, radiation, temperature, and humidity. There are no microphones or cameras, and there is no plan to EVER include such sensors in the future. The purpose of the testbed is primarily for measuring communication and computation characteristics. If you have any privacy concerns about including the testbed in your office, please direct any questions to Dr. Mo Sha.

Acknowledgments

This work is supported by the NSF under a CRII grant (CRII-1657275) and the Binghamton University faculty startup fund.

We thank Prof. Chenyang Lu at the Washington University in St. Louis for sharing the design, implementation, and documents of the testbed and thank Dolvara Gunatilaka for helping us build the implementation.

We thank the Binghamton University, the Watson School of Engineering and Applied Science, and the Department of Computer Science for the administrative support.

We thank our department IT specialist (Dave Hall) and our colleagues at ITS (Joe Roth, Chris Wandell, Andrew Weisskopf, Alan D Wan, John D Frattone, Thomas McCabe, and Scott T Hoeppner) for their help on the testbed deployment and thank Vincent Brady at Engineering Laboratory for building the device cases.